Field of the Disclosure
The present disclosure relates to SiAlON ceramics with enhanced mechanical properties and a method of making these SiAlON ceramics.
Discussion of the Background
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Silicon nitride (Si3N4) ceramics have been shown to withstand severe working conditions due to their remarkable mechanical and thermal properties, namely hot hardness, chemical inertness and thermal shock resistance (Riley, Frank L. Journal of the American Ceramic Society 83.2 (2000): 245-265, incorporated herein by reference in its entirety). However, full densification of Si3N4 powder under the pressure and temperature provided by conventional solid-state sintering techniques has been challenging. The difficulty is attributed to the strong covalent Si—N bond, which resists plastic deformation (Liu, Limeng, et al. Journal of the European Ceramic Society 30.12 (2010): 2683-2689; Belmonte, M., et al. Journal of the European Ceramic Society 30.14 (2010): 2937-2946, each incorporated herein by reference in their entirety). Therefore, Jack and Oyama have developed SiAlON ceramics that are solid solutions of alumina oxide (Al2O3) in Si3N4, in which a portion of silicon and nitrogen is replaced by aluminum and oxygen, respectively (Jack, K. H., and W. I. Wilson. Nature Physical Science (1972): 28-29; Oyama, Yoichi, and Osami Kamigaito. Japanese Journal of Applied Physics 10.11 (1971): 1637, Jack, K. H. Journal of materials science 11.6 (1976): 1135-1158, each incorporated herein by reference in their entirety).
To prepare a fully dense ceramic, Al2O3 is mixed with Si3N4 in the sintering process to form a pure SiAlON ceramic (Cao, G. Z., and Ruud Metselaar. Chemistry of Materials 3.2 (1991): 242-252, incorporated herein by reference in their entirety). Based on the composition of the initial powder mixture and the sintering parameters, several phases, including α-SiAlON, β-SiAlON, O—SiAlON, X—SiAlON or a mixture of them, can form and exist in the SiAlON ceramic (Zhou, Y., et al. Journal of Materials science 30.18 (1995): 4584-4590; Vleugels, Jozef, et al. Institute of physics conference series. No. 130. 1993; Laoui, Tahar, and Omer Van der Biest. Key Engineering Materials. Vol. 89. 1993, each incorporated herein by reference in their entirety). In particular, α-SiAlON and β-SiAlON have attracted attention in the past two decades due to their favorable mechanical properties: high hardness for α-SiAlON and reasonable fracture toughness for β-SiAlON (Izhevskiy, V. A., et al. Journal of the European Ceramic Society 20.13 (2000): 2275-2295; Ekström, Thommy, and Mats Nygren. Journal of the American Ceramic Society 75.2 (1992): 259-276, each incorporated herein by reference in their entirety).
Later, researchers explored other sintering aids to improve the ceramic densification at a lower energy input (i.e. lower sintering temperature and a shorter sintering time) and to produce ceramics with optimal mechanical and optical properties. Lanthanides, such as Nd, La and Yb, have been studied (Herrmann, Mathias, Sören Höhn, and Axel Bales. Journal of the European Ceramic Society 32.7 (2012): 1313-1319; Menke, Yvonne, Valerie Peltier-Baron, and Stuart Hampshire. Journal of non-crystalline solids 276.1 (2000): 145-150; Bandyopadhyay, Siddhartha, M. J. Hoffmann, and G. Petzow. Ceramics international 25.3 (1999): 207-213; Hakeem, Abbas Saeed, Jekabs Grins, and Saeid Esmaeilzadeh. Journal of the European Ceramic Society 27.16 (2007): 4773-4781, each incorporated herein by reference in their entirety). However, the lanthanides have large ionic radii and they poorly occupy the interstitial sites of Si3N4, producing ceramics with crystal defects. In addition, introducing lanthanides into ceramics is also cost-prohibitive.
In view of the foregoing, the objective of the present disclosure is to provide SiAlON ceramics with enhanced mechanical properties and a method of producing these SiAlON ceramics.